Reed switch

ABSTRACT

A reed type electromagnetic circuit switch designed mainly for operation in power circuits of switchgear installations, as well as in automatic control and electric drive systems where the power handled may amount to tens of thousands of voltamperes and rated currents may reach tens and hundreds of amperes; the current circuit of the reed switch is made up of solid current leads, a flexible shunt, and contact tips, manufactured from materials possessing high electrical conductivity. The arrangement includes an armature consisting of a ferromagnetic reed member and thinner ferromagnetic strips and provides for high electromagnetic pull and contact pressure, while a shield and a loop increase the reliability of the reed-to-reed insulation in the off-position and make it possible to develop most reliable and wear resistant contactors. An electromagnet is arranged to attract the armature, and has poles which are introduced into a sealed casing, while the coil of the electromagnet is disposed outside the casing.

Koblents et al.

[ 1 REED SWITCH [76] Inventors: Mark Germanovich Koblents, ulitsaDanilevskogo, 20, kv. 92; Gennady Feodosievich I Mitskevich, ulitsaChernyshevskogo, 95, kv. 58; Eduard Jurievich Polovets, Moskovskyprospekt, 196/1, kv. 60; Anatoly Fedorovich Zhevago, Stadionny proezd,6/6, kv. 13, all of Kharkov, U.S.S.R.

[22] Filed: Oct. 7, 1971 [21] Appl. No.: 187,312

[52] US. Cl. ..-...,..3l7/l55, 200/144, 317/11, 335/151,335/154 [51]Int. Cl....'..; ..H01h 47/04, 1101b 51/28 [58] Field ofSearch.-..335/l5l, 154, 153; 200/144 B; 317/155, 11

[56] References Cited UNITED STATES PATENTS 2,037,535 4/1936 Rankin..335/l54 3,236,965 2/1966 Dal Bianco et al. ....335/l54 3,253,0975/1966 Wagar ....335/l53 3,317,869 5/1967 Funke ..335/l54 IIIIIIIIIIII 7Jan. 16, 1973 [57] ABSTRACT A reed type electromagnetic circuit switchdesigned mainly for operation in power circuits of switchgearinstallations, as well as in automatic control and electric drivesystems where the power handled may amount to tens of thousands ofvoltamperes and rated currents may reach tens and hundreds of amperes;the current circuit of the reed switch is made up of solid currentleads, a flexible shunt, and contact tips, manufactured from materialspossessing high electrical conductivity. The arrangement includes anarmature consisting of a ferromagnetic reed member and thinnerferromagnetic strips and provides for high electromagnetic pull andcontact pressure, while a shield and a loop increase the reliability ofthe reed-to-reed insulation in the off-position and make it possible todevelop most reliable and wear resistant contactors. An electromagnet isarranged to attract the armature, and has poles which are introducedinto a sealed casing, while the coil of the electromagnet is disposedoutside the casing.

8 Claims, 16 Drawing Figures PATENTEDJANIBIQB 3 711 749 SHEET 2 [IF 6 MIll/Ill PATENTEDJAH 16 I975 SHEET [1F 6 PATENTED JAN 16 ms SHEET 5 OF 6Illllll XIV FIG. /4

PATENTEDJAN 16 I975 SHEEI 8 OF 6 F/E. I5

REED swrrcn BACKGROUND OF THE INVENTION 1. Field of the Invention Thepresent invention relates to electric circuit switching devices and,more particularly, to reed switches with ferromagnetic reeds, designedmainly for operation in power circuits of switchgear installations, aswell as in automatic control and electric drive systems where the powerhandled may amount to tens of thousands of voltamperes and ratedcurrents may reach tens and hundreds of amperes.

2. Description of Prior Art Most known reed switches, also termed reedrelays, usually comprise a sealed casing or container and two lightferromagnetic reed members mounted in the casing and disposed to beunder the effect of a magnetic field whereby said reed members movetheir free ends functioning as contact members over a short distanceequivalent of parts per ten and hundred of a millimeter creating acontact pressure of about 30 g.

Such reed switches have lately found a wide application in anumber ofbranches of light-current engineering and have been acknowledged asreliable contact devices noted for high mechanical wear resistance, fastresponse, high insulation resistance, reliability and many otheradvantages which warrant using them to better advantage in conjunctionwith up-to-date semiconductor devices and even as substitutes of thelatter.

A disadvantage of the known reed switches is their low rated current,low power handled and low maximum switching capacity which does notexceed 100 VA for large-scale produced designs and 500 VA for specialdesigns.

Further, in spite of the afore-mentioned advantages of the known reedswitches, and also the possibility of providing a sealed construction,because of their low rated current and limited maximum switchingcapacity they cannot be used as final elements of logic systems or aspower and auxiliary contacts of contactors and starters in electricdrive automatic control systems and as contacts of relays where power tobe handled may amount to tens of thousands of voltamperes and ratedcurrents may reach tens and hundreds of amperes.

Such low rated currents and switching capacity of known reed switches iscaused by extremely small distances over which the contacting surfacesmove, determining contact separation and follow through, as well as bylow contact pressure.

It is not feasible to increase contact pressure, separation and followthrough in the reed switches built according to conventional principlesof design. If we increase the sectional area of the reeds in order toobtain a higher contact pressure and if we provide a larger air gapbetween the free ends of the reeds so as to place solid contact tipsand, hence, to provide high switching capacity, then it will beimpossible to increase the electromagnetic pull to overcome the opposingforce due to the following factors:

a. the magnetic flux closes through the air gap before reaching theferromagnetic reeds, which involves high leakage fluxes and requiresvery large megnetomotiv forces to overcome them; I

b. the sectional area of the reeds is limited as their saturationrestricts the flux traversing the operative air gap and, hence, theelectromagnetic pull between the contact members.

Taking into account that the opposing force is proportional to the thirdpower of sectional area of the ferromagnetic reed, and theelectromagnetic pull is proportional to the first power of sectionalarea, it becomes evident that the reed switches with larger sectionalareas of reeds will fail to operate.

Besides, materials and sectional areas of current-carrying parts in theexisting reed switches are not suitable to pass heavy currents.

Known in the art is a reed switch disclosed in US. Pat. ('cl.335l53)No.3,253,097 comprising a sealed casing accommodating two lightferromagnetic reeds, as well as a coil and a guide member mountedoutside the vessel. An additional external guide member provides for areduction in the flux leakage and makes it possible to obtain therequired magnetic flux applying a reduced magnetomotive force.

This construction may not always provide desirable results since evenwith the external guide member the flux passes on its way through verylarge stray nonoperative air gaps.

SUMMARY OF THE INVENTION It is an object of this invention to provide areed switch which is simple in design and is distinguished by highcontact pressure and contact travel so as to make it possible to operateat large rated currents and to handle high power.

It is another object of this invention to provide contactors builtaround new reed switches characterized in high wear resistance.

This invention aims at providing a switching device built around reedswitches ensuring long service life due to its new constructionalsolution.

This is achieved in that in a reed switch comprising at least twocontact members, of which at least one includes a resilientferromagnetic member, accommodated within a closed casing with at leastone guide member fixed on the latter; one end of the guide membercarries a coil, and is fixed, according to the invention, with the endof the resilient contact member and with a first long solid current leadmade from highconductivity material, while the other end, forming anoperative air gap together with the resilient ferromagnetic contactmember, is accommodated within the vessel at a distance from the contacttips, while the resilient contact member is shorted out with a flexiblecable, one end of the latter being connected to the current lead and theother current lead being made from solid high-conductivity material.

It is another feature of this invention that the casing consists of atleast two complementary parts one of them being made from metal andconnected to that end of the guide member which is accommodated withinthe vessel, while the other part is made from insulating material, andthe resilient contact member presenting a single ferromagnetic stripcarrying a contact member tip is fitted with at least two resilientferromagnetic strips of smaller thickness and length to form a stack,each strip being fixed at one end to the butt end of the guide memberand the entire stack being supported by the extension of the longcurrent lead, the surface of said butt end of the guide member beingdisplaced rela tive to the surface of the other butt end of said guidemember towards the coil.

It is still another feature of this invention that the part of thecasing made from insulating material and having in its section the shapeof, say, a loop, is secured to the metal part of the vessel so that theend of the latter partially shields the insulating casing from the tipsof the contact members; further the butt end of the guide member fixedwith the ends of the resilient ferromagnetic contact member, with thoseof the resilient ferromagnetic strips and with the long solid currentlead is accommodated within the compound metal part of the casing and isjoined with the latter; also the reed switch employs a rectifier and anauxiliary current coil wound on the guide member, all being connectedinto the contact member circuit.

It is therefore reasonable to build around said reed switches acontactor each current pole of which is assembled of one large-powerreed switch and two parallel-connected reed switches of lower power, allforming a single structure.

The reed switches of lower power have a lower dropout time of thecontact tips, hence one of them is closed all the time while itsrectifier is 'conductiv'e'during the half-cycle following theoff-operation of the contactor, ensuring thereby an arclessdisconnection of the load.

The reed switches of this invention have an electric circuit completedby high-conductivity members and a guide member arranged so thatnon-operative (stray) air gaps are practically eliminated. Magnetic fluxpasses to the operative flux of the guide member through ferromagneticcontact members only, and the sectional area of the ferromagnetic reedsdoes not limit the flux contributed to the operative air gap.

All these features have made it possible to obtain a contact pressure ashigh as 1.5 kg, a contact separation exceeding 2.5 mm and a followthrough'over 1.5 mm for experimental models of reed switches rated 63 to100 A, and a contact pressure over 70 g, contact separation exceeding1.5 mm, follow through more than 0.7 mm for models rated 6.3 to A.Experiments carried out with models rated 6.3 to 10 A have shown thateven these small reed switches are capable of handling maximum powerexceeding 10,000 VA. They have high mechanical wear resistance and fastresponse. The models have remained serviceable after more than 150.10operating cycles; their response time at on-operation was within therange of 7 to 10 sec and at off-operation it was about 1 msec.

BRIEF DESCRIPTION OF THE DRAWING This invention will be furtherunderstood from the foregoing detailed description with reference to theappended drawings wherein only specific terms have been selected fordetailed'disclosure; it should be borne in mind, however, that theinvention is not to be restricted by adopted specific terms andthat eachterm embraces all equivalent elements serving the samepurpose in thescope of this invention. I

. It should be also borne in mind that other objects and advantages ofthis invention besides those mentioned above will be further understoodfrom the following detailed description when taken in conjunction withthe accompanying drawings, in which:

FIG. 1 shows an illustration of the mutual arrangement of reed switchbasic components;

FIG. 2 shows the reed switch of FIG. 1 with a sectionalized casing;

FIG. 3 is the reed switch of FIG. 2 with solid current leads andflexiblecable;

FIG. 4 is the reed switch of FIG. 3 with auxiliary thin ferromagneticstrips;

FIG. 5 is a diagrammatic representation electromagnet of the arrangementshown in FIG 4;

FIG. 6 is a diagram showing the position of the ferromagnetic reed whenthe butt ends of the guide member are in one plane;

FIG. 7 is a diagram showing the position of the ferromagnetic reed whenthe butt ends of the guide member are displaced;

FIG. 8 shows the reed switch according to FIG. 4 with additionalprotection off a part of the insulating casing against contact metalsplashes; I

FIG. 9 shows a further embodiment of the reed switch similar to the oneshown in FIG. 8;

FIG. 10 is a modification of the reed switch shown in FIG. 9;

FIG. 1.1 is a constructional form of the reed switch;

FIG. 12 shows an illustration of a contactor built around the reedswitches of the invention;

FIG. 13 is the side view of the contactor of FIG. 12;

FIG. 14 is the plan view of the contactor of FIG. 12;

FIG. 15 is an electric circuit diagram of one pole of an arclessswitching contactor built around reed switches of the invention;

FIG. 16 is an illustration of one pole of an arcless switching contactorbuilt around reed switches of the invention.

Certain other objects and .advantages of this invention besides thosementioned earlier will become apparent from the further detaileddescription with reference to the appended drawings.

The ferromagnetic guide member of the reed switch, according to thisinvention, in distinct from that made in accordance with US. Pat. No.3,253,097, and is arranged so that its one end is tightly fitted to theexternal end of the ferromagnetic reed carrying the movable contact,while the other end is introduced into a sealed casing wherein it isplaced in close proximity to said reed forming thereby an operativemagnetic gap,,and the contacting point of the contact members isdisplaced with respect to the operative magnetic gap in the directionopposite to the point of attachment of said ferromagnetic reed, whichserves at the same time as an armature, the operating coil being woundon the guide member. v

The mentioned guide member, according to this invention, can be made upof a core one endof which is introduced into the sealed casing and ayoke arranged outside of the casing, and the casing can be composed oftwo non-ferromagnetic shells and an insulating (say, glass) tube.

The reed switch arrangement described thereof makes it possible toconsiderably increase contact separation at a relative decrease of therequired magnetornotive force of the operating coil and to employcontact tips made from high wear-resistant material, all this leading toa considerable increase in the switching capacity and electric wearresistance. l

Referring to FIG. 1, there is shown-a reed switch comprising a sealedcasing 1 accommodating contact tips 2 and 3 and a ferromagnetic guidemember 4. The guide member 4 is arranged so that its one end 5 istightly fitted to the external end of the light ferromagnetic reed 6carrying movable contact 2, and its other end 7 is introduced into thesealed casing l and placed in close proximity to the reed 6 between thepoint of attachment of movable contact 2 and the point of fastening ofsaid reed within the vessel 1. An operating coil 8 providing for therequired magnetomotive force is wound on the guide member 4.

With this arrangement of components, as distinct from the known designsof reed switches, flux passes to the operative air gap of the guidemember (between the ferromagnetic reed 6 and the end of the guide member7 attached within the casing ii) through ferromagnetic components overits entire path (since non-operative stray air gaps are practicallyeliminated) which minimizes leakage fluxes and substantially reduces theamount of magnetomotive force required for moving the contacts andcreating the required contact pressure.

Due to the relative displacement of the guide member air gap and the airgap between the contacts it has become possible to minimize theoperative air gap of the guide member and to considerably increase theair gap between the contacts which ensures a high switching capacity ofthe device.

It is easily understood from FIG. 2 that in order to provide for theadjustment of the guide member operative air gap determining the contactseparation and follow through as well as to improve their heatdissipation, the casing 1 (FIG. ll) can be made of two non-ferromagneticshells 9 and 10 joined by means of an insulating (say, glass) tube ill.

To improve the mechanical design of the device, the guide member 4 canbe composed of a core portion 12 (FIG. 2) inserted with its one end intothe shell of the sealed casing 9, and a yoke portion 13 placed outsideof the casing.

The reed switch operates as follows. When power is supplied to theoperating coil 8 a magnetic flux is set up in the magnetic circuit ofguide member 12, 13 under the effect of the magnetomotive force. Thismagnetic flux passes through the guide member and the ferromagnetic reedor armature 6 bearing a contact tip 2 and is concentrated in theoperative air gap of the guide member. As a result, an electromagneticpull is created within this air gap which causes the reed 6 to strainand to shift the movable contact member 2 secured on its end until it isclosed with the fixed contact member 3.

As soon as the operating coil 8 is deenergized, the reed 6 returnsresiliently to the initial position under the effect of opposing forcesand opens the contact members.

It is a well-known fact that the rated current of exist ing reedswitches is limited because of heavy power loss and extremely highheating of the switching device caused by high resistance ofcurrent-carrying parts (which have low electrical conductance) becausethese parts serve as guide members for magnetic flux and are electriccontacts at the same time.

These drawbacks have been eliminated in the reed switch of thisinvention by shorting out the ferromagnetic reed accommodated within asealed casing and carrying a movable contact by means of a flexiblecopper shunt 14 (FIG. 3).

One end of the shunt is connected (soldered) directly to the contact tip2 and the other end to the output current lead of the movable contact 16whose end is brought inside the vessel and is used also as the retainerof the reed (or armature) travel. Placing the armature retainer withinthe casing has given an additional possibility of reliably adjusting thearmature angle of turn determining the contact separation and followthrough in the course of assembling the switching device before puttingon the glass tube.

The part carrying the fixed contact, as well as the current lead of themovable contact are made from high-conductivity material, such ascopper.

Hence, along with above-mentioned advantages, all the current circuitcomponents of the device of this invention are made fromhigh-conductivity materials which makes it possible to reduce Joule lossand to increase the rated current of the switching device.

Mentioned advantages have been achieved by rendering solid contacts, asingle movable component being comprised in the guide member, dispensingwith a solid ferromagnetic block, which has improved the response of thedevice.

The solid movable contact (tip) 2 placed within a sealed casing 9, l0,11 (FIG. 3) is fixed on a flat ferromagnetic reed 6 which serves as anarmature of the guide members 12, 13 which are part of a magneticcircuit. The ferromagnetic reed 6 is shorted out by means of a flexibleshunt 14 made from a copper bunched conductor whose one end, as has beenmentioned, is soldered or welded to contact 2 and the other end with thearmature travel retainer 15 which also serves as the external lead 16 ofthe movable contact made from a material possessing high conductivityand mechanical strength. The part 17 carrying the solid fixed contact(tip) 3 is also made from a material having high conductivity andmechanical strength and serves at the same time as an external lead 18of the fixed contact.

The armature travel retainer 15 provides for a more reliable adjustmentof the operative air gap 19 in the guide member while assembling theswitching device.

When the coil 8 is energized, the armature 6 is pulled in and thecontacts 2, 3 close passing the current in the power circuit throughcomponents possessing high electrical conductivity (the current path isindicated by arrows). The current branched off to the ferromagnetic reed6 is negligible as the resistance of the latter is much higher than theresistance of the flexible shunt 14.

A considerable decrease in the resistance of the current circuit ascompared to the known arrangements, has made it possible to develop reedswitches for high current ratings.

In order to make the contact suitable for carrying heavy currents,however, it is necessary to ensure, accordingly, a high contactpressure.

As has been stated above, a mere increase in the thickness of theferromagnetic reed carrying the contact member will not give necessaryresults, as the opposing torque will increase with contact pressure andthe electromagnetic torque will rise negligibly due to the fact that thesectional area of the electromagnet armature (flat reed) varies to asmall degree. Therefore, the sectional area of the reed cannot beselected arbitrarily as it should be determined by the selected contactpressure.

In selecting the size of the reed, taking into account the mentionedconditions, the sectional area of the reed is usually much less thanthat of the fixed part of the guide member which makes the armatureheavily saturated and confines flux, and consequently, electromagnetictorque, in the operative air gap.

As is known, the sag of the flat reed where l is the distance from thepoint of attachment of the reed to the point of force application;

x is the distance from the point of attachment of the reed to thesectional area concerned;

E is the material modulus of elasticity;

y is the inertia moment of the reed sectional area.

where b is the reed width;

h is the reed height.

Upon consideration of the above equations it becomes evident that theforce created by the reed on arm 1 Sectional area of the reed S bh.

Hence, the force created by the reed varies as the cube of itsheightwhereas its sectional-area is proportional to the first power ofthe height.

It follows from the above considerations that a small increase in thethickness of the reed causes a considerable increase of the opposingtorque developed by the reed at a substantially smaller increase of itssectional area. The opposing torque, therefore, will rise more rapidlythan the electromagnetic torque and the electromagnet will fail tooperate if the thickness of the ferromagnetic reed is increased. Toreduce the armature saturation and at the same time retain all theadvantages of devices comprising ferromagnetic reeds, it is preferred toemploy" one reed ensuring the required opposing torque and to placethinner ferromagnetic reeds in parallel to the former. Such anarrangement will ensure a considerable increase in the electromagnetictorque since the armature saturation will decrease andthe flux in theoperative air gap will increase with the increase of the armaturesectional area, the opposing torque being practically the same.

As an example we may take an arrangement in which five ferromagneticreeds are set in parallel to the main reed, each of the former beingtimes thinner than the latter. Then the armature sectional area will betwice as large and the, opposing torque (force) will rise 1.04 timesonly since n=5 h 3 Mn Kh +Kz(-) I 5 1+5 Z -104 Kha 5 Replacing a solidarmature by one built up of separate ferromagnetic strips arranged inparallel to the butt ends further of the guide member fixed part andrigidly secured at one end increases the shock and vibration resistanceof the device.

Besides, eddy currents arising in the armature at the moment theelectromagnet coil is switched on or off are decreased thus reducing theopening and closing time of the device.

Referring to FIG. 4 and FIG. 5 there is shown an arrangement in whichone of the ends of flat ferromagnetic reeds 6, 20, 21, 22 (the number ofreeds may be much greater than indicated) is rigidly secured at the buttend 5 of the fixed part of the guide member 13 carrying the coil 8 sothat in the open position an operating air gap 19 is set up between thebutt end 7 and the extreme reed 6, the magnitude of said air gap beingfixed by the retainer 15 which provides for the preliminary tensionensuring that in the off position all the reeds within the operative airgap are pressed tight to each other. Therefore, a smaller amount ofmagnetomotive force'is required for conducting the flux through the airgap.

When the pull-in coil is energized, the flux passed to the air gap issharply increased due to additional strips increasing the sectional areaof the armature.

The contact tip 2 is secured to the main (thick) ferromagnetic reed 6and the thin ferromagnetic reeds 20, 21, 22 are fixed on one end and arefree to move on the other end. I

If the butt ends 5 and 7 of the guide member are placed in one plane, asshown in FIG. 6, the reed will come in contact with the core on one sideonly (on the right) while on the other side an air gap 23 will be set upbetween the reed and the core. If the electromagnetic pull is muchgreater than the force of the reed, then the latter may get fullyattracted to the core, but in this case inadmissible internal strainwill be produced in the reed causing residual deformation, a change inits settings and a reduction of its operational reliability.

Besides, too large an air gap in the pulled-in position of the armature(reed) will increase the total air gap in the off-position and decreasethe conductance of the operative air gap and the electromagnetic torque.Then higher ampere-turns will be required to obtain the necessarycontact separation, follow through, and pressure.

It is, therefore, preferable to fix the reed at a point located inrespect tothe core as illustrated by FIG. 7 so that in the pulled-inposition there is no apparent air gap between the reed and the core.This can be achievedby shifting the reed axis from point 0 to point 0,over a distance A, ref.24 (FIG.7); in such a case air gap 8 y,, ref.23(FIG.6) will be eliminated.

From calculations and investigations it was found that the reed fixingaxis should be optimally shifted relative to the plane crossing theoperating surface of the core over a distance A equal to a half of theair gap 8 p between the operating surface of the core and the reed,

In the course of prolonged use of reed switches and after a great numberof on-off operations, splashes of molten contact material may getdeposited the insulating (glass) tube causing a gradual bonding of theinner surface of the glass tube, which may result in a decrease ofelectric strength and insulation resistance between the contact membersin the open position.

In order to decrease the efiect of this factor, the contacts are madefrom hard materials having high melting points. In such a case thecontact material will not splash but the contact resistance mayincrease. To use softer materials for contacts providing a much lowercontact resistance, provision should be made for shielding, at leastpartially, the contact members so as to prevent splashes of moltencontact material from getting on the glass insulating one contact fromanother.

The reed switch of this invention has a shield protecting the insulatingglass from metal splashes made from the structural components of thedevice proper so as to dispense with additional parts and complicationof mechanical design.

The metal housing 9 (FIGS) carrying the flat ferromagnetic reed 6 andthe core 12 serves as a shield protecting the glass enclosure 11 fromsplashes of molten contact material. Part of the housing 25 located onthe side of the core 12 is set at a distance and braces with its end thecontacts 2 and 3. The glass enclosure 11 is secured on the outside ofthe housing 9 at a distance of 8 from the edge. The enclosure isessentially a glass tube widened in the middle so that a space isprovided between the outer surface of the vessel and the inner surfaceof the widened'portion of the glass tube on length 8,. This space ishard for molten metal splashes to get at. In this way the insulationreliability upon wear of contacts is improved without complicating themechanical design of the switching device.

In order to obtain a still greater reliability of insulation upon wearof contacts, the glass vessel 11 (FIGS) is made in the form of a tubewidened in the middle and looped on length 8,. In this case a muchgreater area of the inner surface of the vessel is protected againstmolten metal splashes, the length of this area being equal to Tofacilitate observation of the contacts while the switching device isassembled, the metal housing is made longer by a value of 8, 8 as shownin FIG. so that it does not close the contacts.

At the same time, the loop 8, is made longer to provide betterprotection of the vessel against molten metal splashes. Due to thismeasure the' vessel surface to be protected remains unchanged:

while the contacts are now easily observed in the course of assembly andadjustment of the switching device.

The device operates as followsswhen the coil 8 is energized, the flatferromagnetic reed or armature is pulled in tothe core. 12, and thecontacts 2, 3 close. As soon as the coil is deenergized, the armaturedrops out and the contact members start separating. An electric areformed between theseparating contact melts the material of the contactswhich splashes in all directions and may get on the metal and glassportions of the housing. But since the metal vessel and the glass loopare elongated, the major portion of the inner surface of the glass tube11 is protected against these splashes.

To improve sealing of the switching device and to simplify itsmanufacturing technique, the ferromagnetic strips should be arrangedwithin the casing and all the components of the device should be joinedtogether by metal-to-metal welding or soldering. This can be achieved inthe reed contact by introducing the other butt end of the guide memberinto the vessel, by sectionalizing the metal casing and by terminatingthe insulating tube with suitable metal (or an alloy such as Kovar)soldered to the end faces of the glass tube.

As distinguished from the arrangement considered earlier, this devicehas a sectionalized metal casing made from a non-ferrous sleeve 26(FIGJI) and a disc 27 at the bottom of the sleeve. Coupled with thesleeve 26 are two ferromagnetic core members 12 and 28 which havesimilar ends 7, 29 placed within the sleeve and the other end 30, 31outside of the sleeve. The end 7 of one of the cores is arranged, likein reed switches referred to before, in close proximity to theferromagnetic reed 6 forming thereby an operative air gap, while theother end 29 of the core inserted into the sleeve 26 is tightly fittedto the end of the ferromagnetic reed 6 carrying the contact tip 2. Thissame core end 29 bears thin ferromagnetic strips 20, 21, 22 and a longsolid current lead of the movable contact 2, one end 16 of this leadbeing passed through the pole in the disc 27 outside of the vessel whilethe other end 15, with a flexible stranded conductor 14 attached to-it,serves as a bearing surface for the strips 22, 21, 20, these stripsfunctioning as the electromagnet armature.

Attached to the core ends 30 and 31 passed outside of the vessel is ayoke 32 which carries a wound coil 8.

The insulating portion of the vessel (11) made from, say, glass iswelded at the ends to metal (Kovar) rings 33 and 34.

The ring 34 is joined with the disc 35 to form another shell of thecasing. Another solid current lead 18 carrying the contact tip 3 ispassed through the hole in the disc 35. The other end of the ring 33built integral with the insulating portion of the casing 11 is rigidlyfixed with the sleeve 26, after the contact separation, follow throughand pressure have been adjusted, so that the glass portion arrangedbehind the end of the sleeve 25 is out of reach of metal fragments whichmay appear when heavy currents are handled by the contacts.

The development of reed switches with an independent operatingelectromagnet for each contact pair suitable for operation in electricpower circuits has made it possible to construct unique designs ofcontactors which, in the first place, can operate in differentatmospheres containing dust, gases, and other aggressive or corrossiveagents which otherwise (in non-sealed designs) might impair switching;in the second place, the reed switches of the invention have amechanical wear resistance at least one order higher than all knowndesigns of contactors; and in the third place, these reed switchesintroduce new aspects in the construction of automatic control electricdrive systems due to the absence of any mechanical tie between themovable contact members of separate contacts fulfilling commonfunctions.

Referring to FIGS. 12, 13, 14', there is shown the mechanical design ofa three-pole contactor rated A and built around reed switches of theinvention. This contactor can be used for starting and stoppinglightpower induction motors.

Since the electromagnet core 12 is placed partially within the casingand partially outside of it, the winding 8 can be arranged outside so asto be common for all the poles. Three reed switches 36, 37, 38 aresecured on an insulating base 39 Each contactor consists of a casingaccommodating a fixed contact assembly 3, a movable contact assembly 2(functioning at the same time as an armature), and a portion of the core12.

i 2 A simpler circuit arrangement can be obtained by firing thethyristors from the auxiliary contacts of the contactor proper. In sucha case, however, the contactor the coil former. The coil former isfitted with holes 42 and 43 intended to receive light-power reedswitches 44, 45 which are used as auxiliary contacts. The entire deviceis housed in a common casing closed with a cover 46 which is put on thebase 39. I

The contactor operates as follows. Whenthe operating coil 8 isenergized, magnetic flux is set up at allthe poles simultaneously. Thisflux traverses the cores 12 and the ferromagnetic reeds 6 which functionas arma-' tures and contact holders, causing an electromagnetic pull inthe operative ,air gap. As a result, the contacts close. Simultaneouslyoperate the reed switches placed inside the coil former and excited bythe magnetomotive force of the operating winding.

When the operating coil is deenergized, the movable contacts orarmatures of all the poles as well as the reed switches functioning asauxiliary contacts are reset to the initial position.

As thecoil is common for all the poles, its ampereturns will remainunchanged irrespective of the number of poles, the sectional area of themagnet wire and the space factor, as well as the cooling surface of thecoil can be increased causing a decrease in the coil heating,simultaneous operation is ensured and the device reliability isimproved. In manufacturing contactors built around power reed switchesand designed to control high-power circuits (including those ofhigh-power A.C;motors), it is good practice to make provision forarcless off-operation to ensure high electrical wear resistance ofcontacts. Power reed switches introduce new aspects in the developmentof arcless switching devices.

The most reliable in operation of all known arcless switching contactorsare those wherein their power contacts shorted out by two powerthyristors connected in parallel opposition and start passing current atthe instant the power contacts separate and are deenergized at themomentthe current passes zero. In such contactors firing of thyristorscan be effected by applying av transformed and rectified power circuitcurrent to the control electrode; such an arrangement involves a rathercomplicated control system employing a great number of auxiliaryelements.-

mechanical design should be of utmost reliability as to the operatingsequence of power and auxiliary contacts; as the contactor wears down,its contacts tend to get maladjusted and the system fails. Itis just forthis reason that such an arrangement has not found a practicalapplication.

In addition to the mentioned disadvantages of arcless switching circuitsin which the power contacts are shorted out by thyristors (or any otherrectifiers), their essential drawback consists in the absence ofelectrical decoupling of circuits in the off-position of the contactor(the rectifiers will pass leakage currents). This calls for theconnection of disconnecting switches or other similar devices in serieswith the power contacts.

Electrical decoupling of circuits in arrangements where the powercontact are shorted out by rectifiers connected in parallel oppositioncan be achieved by inserting the .auxiliary contacts of the contactorsin series with the rectifiers. In such an arrangement an appropriatesequence of separation of the power and auxiliary contacts of aparticular pole is essential to ensure anarcless opening of electriccircuits.

All the known contactors employing diodes for arcless switching have acommon electromagnetic operating mechanism which operates both power andauxiliary contacts of the particular pole. Therefore, the

required sequence in contact separation is achieved by mechanical means:appropriate adjustment of contact follow through, setting ofmiscellaneous latches, special electromagnetic locks, etc. With a commonoperating mechanism; these mechanical ties between contacts (and thelatter are subject to wear and maladjustment) cause a considerablereduction of mechanical wear re sistance and reliability ofmechanical'design; hence, such arrangements have not found practicalapplication.

The known arcless switching contactors have a single operating mechanismirrespective of the number of poles which actuates a shaft or acrosspiece coupled with the movable members of the power contacts. Tothis end, a special form of design of the shaft, crosspieceand otherparts should be available for each contactor design according to thenumber of poles (one, two, three, four, five).

Besides, a single electromagnet common for all designs is usually ratedfor the maximum number of poles; therefore single-pole and two-polecontactors are made conservative which leads to extra expenditure ofmaterials andpower.

In known contactor designs arcless switching is aforded by theabove-mentioned method with the aid of special attachments-to standardcontactors. This makes the contact assembly of a standard contactor toocomplicated.

The power reed switches used. in contactors will make it possible todevelop a contactor in which arcless switching is achieved without. anymechanical tie between the contacts of different poles and betweenseparate contacts of one pole as each pole contact (both power andauxiliary), is fittedwith a separate electromagnetic operatingmechanism, the operating sequence of contacts being afforded byelectrical, and not mechanical, coupling. v

FlG.15 illustrates an electric circuit of one pole of a heavy-currentpower contactor.

Each pole of this contactor is a self-contained unit comprising onehigh-power reed switch 47 rated continuously to carry the power circuitrated current and two auxiliary reed switches 48, 49 having a muchhigher resistance of the current circuit and a little longer inherentopening time than the reed switch 47, and consequently, a smaller sizeand current rating which makes up to per cent of the power circuit ratedcurrent. Diodes 50 and 51 as well as hold-in current coils 52 and 53 areconnected in series opposition to each auxiliary contact 48 and 49.

The current circuits of the auxiliary contacts are connected across thepower contact 47. The turns of the hold-in current windings 52 and 53mounted on the guide members 54 and 55 are wound in such a way that atthe instant the power contact 47 opens (the auxiliary contact 48 or 49starts passing the respective half of the power circuit current) theflux produced by the hold-in coil 52 and 53 is in added relation withthe flux created by the respective D.C. pull-in coil 56 or 57 mounted onthe guide member 54 or 55, respectively. It is preferable to connect thepull-in coil 59 of the high-power reed switch 47 mounted on the guidemember 54 in series with the pull-in coils of the auxiliary contacts 48and 49 to exclude non-synchronous off-operation upon the occurrence ofan open circuit in one of the coils.

All the poles of multipole contactors have a similar design.

The device operates as follows.

When the control circuit is connected to a DC. supply, the armatures ofall the three electromagnets 58, 54, 55 are pulled in, the contact tipsof the contacts 47, 48, 49 close and switch on the load. The loadcurrent will flow mainly through the power reed switch 47 which has amuch higher contact pressure and a much lower contact resistance, thanthe tips of the auxiliary reed switches 48, 49.

Disconnection of the control circuit deenergizes the coils 59, 56,and57; the armature of the electromagnet 58 holding the contact tips ofthe power reed switch 47 as well as the armature of one of theelectromagnets holding the contact tips of the auxiliary reed switchwhose diode is cut off at the particular half-cycle (say, theelectromagnet 54 holding the contact tips of the reed switch 48) dropout. Then the armature of the electromagnet 55 will be held by the fluxset up by the hold-in coil 53 as the diode 51 will pass current at theparticular half-cycle. The contact tips of the reed switch 49 willremain closed and will pass all the power circuit current as the contacttips of the reed switches 47 and 48 are open.

As soon as the instantaneous value of current in the half-wave passed bythe diode 51 decreases, the flux created by the hold-in coil 53 reducesand when the current approaches zero, the armature of the electromagnet55 drops out; as a result, the contact tips of the reed switch 49 open.During the next half-cycle the diode 51 is cut off; thus the danger ofits repeated firing and armature attraction is excluded.

A similar process will take place in the circuit of the reed switch 48in case the reed switch 47 opens at the instant the diode 51 is cut offand the circuit of the reed switch 49 does not pass current.

Hence, the device of this invention is suitable for disconnecting theload at the instant the instantaneous value of current approaches, or isequal to, zero providcan be used to make up a contactor for any desirednumber of poles dispensing with additional special parts.

Such an arcless switching contactor will be characterized in high degreeof reliability, low power requirement, short operating time, and lowcost.

What is claimed is:

li. A high-power reed switch for switching an electric circuit,comprising: a casing and at least two contact members arranged thereinin apposition, the first of said two contact members being fixed andhaving a high conductivity lead, the second of said two contact membersbeing movable; a magnetic member provided with means to induce magneticflux therein and having an open frame-like configuration with twosubstantially parallel butt end faces formed at the ends of two spacedlimbs of the magnetic member; a resilient ferromagnetic elongated membersecured at one end thereof to said second contact member and secured andcantilevered at the other end thereof with the first of said two buttend faces, said resilient elongated member being so disposed as to forman air-gap at a switch OFF position between said elongated member andthe second of the said butt end faces, said air-gap being at a distancefrom said two contact members; and a second high conductivity leadpassing through said casing and having a flexible conductive leadattached to the second high conductivity lead at one end thereof and tosaid second movable contact member at the other end, whereby saidresilient ferromagnetic elongated member forms part of an uninterruptedmagnetic circuit provided by said magnetic member so as to minimizeleakage flux, and increase the switch current rating in view of saidflexible lead.

2. A'high-power reed switch for switching electric circuits, accordingto claim 1, in which:

said casing is made up of at least two end parts and a middle part, thefirst of said two end parts being metallic and being coupled with partof said magnetic member whose said first butt end face is accommodatedwithin the casing, the middle part of the casing being made frominsulating material.

3. A high-power reed switch for switching electric circuits, accordingto claim 2, in which:

said resilient ferromagnetic member is made in the form of a singleferromagnetic strip carrying said second contact tip, and is fitted withat least two further resilient ferromagnetic strips of lower thicknessand length to form a stack, each strip being fixed with its one end tosaid first butt end surface, while the entire stack rests upon theprojection of an elongated current lead, said first butt end surfacebeing displaced relative to the second butt end surface in a directionaway from said contact-members.

4. A high-power reed switch for switching electric circuits, accordingto claim 3, in which:

said part of the casing made from insulating material is shaped in itssectional region to form a loop, and wherein the insulating part isfastened to the metal casing so that its end partially shields theinsulating part of the casing from the contact tips. 5. A high-powerreed switch for switching electric circuits, according to claim 4, inwhich:

said first butt end surface fixed with the ends of the single resilientferromagnetic strip and said at least two further resilientferromagnetic strips, as well as said elongated current lead areintroduced into and coupled with said metallic first end part of thecasing. 6. A reed switch according to claim 4, wherein said means toinduce magnetic flux in said magnetic member comprises a d.c. coil, thereed switch further including a rectifier, an an additional currentwinding wound on said magnetic member, said rectifier and saidadditional current winding being connected in series with said first andsecondcontacts, so that said additional current winding aids themagnetic flux in the magnetic member, and upon connection of the reedswitch to an a.c. line, the flux due to the additional curseparatedwithout chattering.

7. A reed switch as in claim 1 wherein said means for inducing magneticflux in said magnetic member comprises d.c. coil capable of producingmagnetic flux simultaneously in a plurality of reed switches, and saidresilient ferromagnetic elongated member forms part of an uninterruptedmagnetic circuit in an ON position of the reed switch.

8. A contactor assembly for an a.c. circuit, including a high-power reedswitch as in claim 7, and further second and third reed switchesconnected in parallel therewith, said second and third reed switcheseach having an additional magnetizing current coil disposed on thecorresponding magnetic member, and a diode connected in series withcorresponding set of first and second contact members, the correspondingcontact members of the second and third reed switches having an inherentdrop-out time longer than that of said first switch, so that, after anOFF operation of the contactor assembly, one of said second and thirdreed switches remains closed during a half cycle of the a.c. circuitpower when its diode is conductive, providing thereby an arclessinterruption of the a.c. circuit load.

1. A high-power reed switch for switching an electric circuit,comprising: a casing and at least two contact members arranged thereinin apposition, the first of said two contact members being fixed andhaving a high conductivity lead, the second of said two contact membersbeing movable; a magnetic member provided with means to induce magneticflux therein and having an open frame-like configuration with twosubstantially parallel butt end faces formed at the ends of two spacedlimbs of the magnetic member; a resilient ferromagnetic elongated membersecured at one end thereof to said second contact member and secured andcantilevered at the other end thereof with the first of said two buttend faces, said resilient elongated member being so disposed as to forman air-gap at a switch ''''OFF'''' position between said elongatedmember and the second of the said butt end faces, said air-gap being ata distance from said two contact members; and a second high conductivitylead passing through said casing and having a flexible conductive leadattached to the second high conductivity lead at one end thereof and tosaid second movable contact member at the other end, whereby saidresilient ferromagnetic elongated member forms part of an uninterruptedmagnetic circuit provided by said magnetic member so as to minimizeleakage flux, and increase the switch current rating in view of saidflexible lead.
 2. A high-power reed switch for switching electriccircuits, according to claim 1, in which: said casing is made up of atleast two end parts and a middle part, the first of said two end partsbeing metallic and being coupled with part of said magnetic member whosesaid first butt end face is accommodated within the casing, the middlepart of the casing being made from insulating material.
 3. A high-powerreed switch for switching electric circuits, according to claim 2, inwhich: said resilient ferromagnetic member is made in the form of asingle ferromagnetic strip carrying said second contact tip, and isfitted with at least two further resilient ferromagnetic strips of lowerthickness and length to form a stack, each strip being fixed with itsone end to said first butt end surface, while the entire stack restsupon the projection of an elongated current lead, said first butt endsurface being displaced relative to the second butt end surface in adirection away from said contact-members.
 4. A high-power reed switchfor switching electric circuits, according to claim 3, in which: saidpart of the casing made from insulating material is shaped in itssectional region to form a loop, and wherein the insulating part isfastened to the metal casing so that its end partially shields theinsulating part of the casing from the contact tips.
 5. A high-powerreed switch for switching electric circuits, according to claim 4, iNwhich: said first butt end surface fixed with the ends of the singleresilient ferromagnetic strip and said at least two further resilientferromagnetic strips, as well as said elongated current lead areintroduced into and coupled with said metallic first end part of thecasing.
 6. A reed switch according to claim 4, wherein said means toinduce magnetic flux in said magnetic member comprises a d.c. coil, thereed switch further including a rectifier, an an additional currentwinding wound on said magnetic member, said rectifier and saidadditional current winding being connected in series with said first andsecond contacts, so that said additional current winding aids themagnetic flux in the magnetic member, and upon connection of the reedswitch to an a.c. line, the flux due to the additional current windingdies out at the first current zero of the a.c. line and said first andsecond contacts can stay separated without chattering.
 7. A reed switchas in claim 1 wherein said means for inducing magnetic flux in saidmagnetic member comprises d.c. coil capable of producing magnetic fluxsimultaneously in a plurality of reed switches, and said resilientferromagnetic elongated member forms part of an uninterrupted magneticcircuit in an ''''ON'''' position of the reed switch.
 8. A contactorassembly for an a.c. circuit, including a high-power reed switch as inclaim 7, and further second and third reed switches connected inparallel therewith, said second and third reed switches each having anadditional magnetizing current coil disposed on the correspondingmagnetic member, and a diode connected in series with corresponding setof first and second contact members, the corresponding contact membersof the second and third reed switches having an inherent drop-out timelonger than that of said first switch, so that, after an ''''OFF''''operation of the contactor assembly, one of said second and third reedswitches remains closed during a half cycle of the a.c. circuit powerwhen its diode is conductive, providing thereby an arcless interruptionof the a.c. circuit load.